The present invention relates generally to exhaust hoods, and, more particularly, to energy-efficient exhaust hoods for use in commercial kitchens.
Commercial cooking equipment create varying quantities of heat and effluents as a by-product of their cooking processes. For example, a commercial kitchen may have a cook line with burners for cooking pans, deep fryers, griddles, steam tables, and grills. In order to remove waste gas, heat, and/or effluents from the cook line, a commercial kitchen typically includes a kitchen ventilation system. Such a kitchen ventilation system typically includes an exhaust assembly that exhausts air collected in an exhaust hood. In many instances, a source of supply air delivers make-up air into the kitchen.
Many known exhaust hoods are installed above cooking equipment so as to position their collection region to capture effluents generated by the cooking equipment. Such exhaust hoods typically draw exhaust air from the collecting region through a filtering device that separates the collecting region from an exhaust chamber. The exhaust chamber is typically connected to an exhaust duct, which is typically connected to an exhaust fan. Known exhaust hoods may also include an internal or external make-up air chamber facilitating the total or partial delivery of make-up air.
A typical commercial kitchen has a variety of types of cooking equipment (e.g., burners for cooking pans, deep fryers, griddles, steam tables, and grills). Often, the cooking equipment is aligned side-by-side to form one continuous cook line. As a result, the cook line may place varying cooking techniques, temperatures, fuels and loads next to each other. It is also typical for a single exhaust hood to be installed over the cook line made up of varying cooking equipment.
The design and specifications for kitchen ventilation systems, much like other ventilation systems, are guided and governed by various standards (e.g.; architectural; American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE); and Underwriters Laboratories (UL)). The challenges of ventilating a cook line with varying cooking equipment, temperatures, fuels and loads have been well documented. A common technique for designing and operating an exhaust hood over a cook line involves “over powering” the hood, whereby the ventilation system and its associated exhaust hood are engineered to be more than capable of meeting the worst case scenario that could possibly arise for the capture and containment of the cooking equipment's plume. This approach, while technically adequate from a plume capture and containment perspective, is far from being energy efficient. For example, an exhaust hood designed to handle the exhaust from grilling twenty steaks and an equivalent amount of potatoes in the deep fryer as side dishes for the steaks might be used when only a single egg is being cooked for a breakfast dish.
The need for more energy efficient kitchen ventilation systems that provide a safe and comfortable working environment have necessitated an entire rethinking of the over powering method. For example, U.S. Pat. No. 4,286,572 discloses a ventilating hood that includes an air supply assembly. The air supply assembly directs substantially all of the air incoming to the hood toward the exhaust filter of the hood, and a minor segment of the air flow substantially downwardly for creating an air shield above the frontal portion of a heating apparatus (e.g., a cooker). The incoming supply air is used to help urge the fumes toward the filter. However, in operation, such an exhaust hood may have less than ideal operating characteristics. For example, the flow rate of exhaust air required to capture and contain the heat and effluents from the cooking equipment may actually have to be increased to overcome the added short circuit air, the space that it occupies, and the turbulence that it creates, thus using more energy, not less, and hindering, not improving, the surrounding kitchen environment.
U.S. Pat. No. 4,811,724 discloses a ventilating hood that includes a blow chamber. The blow chamber directs a plurality blow jets to induce secondary air jets. The blow jets are utilized to assist in the capture and containment of the exhaust effluents. Although the design allows for the ability to adjust the total volume of air being supplied to the blow jets, it does not allow for the individual adjustment of the blow jets, thus the blow jets cannot be adjusted to meet varying characteristics of the plume in different sections of the hood. The lack of adjustability of the blow jets also may make it difficult to maintain a beneficial relationship between the flow rate of the supply air and the speed of the blow jets when making adjustments to the total supply air flow rate. Again, in operation, such a hood may fall short of achieving a significant reduction of exhaust flow rates, and of effectively and efficiently exhausting fumes.
Therefore, improved exhaust hoods that can effectively exhaust kitchen fumes are desirable, especially exhaust hoods that can exhaust kitchen fumes in an energy efficient manner.